This study is designed to obtain information applicable to developing a detailed explanation of the molecular processes involved in photoreceptor function. Visual pigments represent a class of intrinsic membrane proteins, whose retinal chromophore serves as a receptor site for photons. Of particular interest in this study is the transduction step in which a photon absorbed by rhodopsin results in a hyperpolarization of the rod outer segment plasma membrane. A major aim of this proposal will be to elucidate the role of the membrane microenvironment in modulating the transduction process. Information bearing on transduction will be obtained by correlating such membrane properties as microviscosity and phospholipid head group and acyl side chain composition with rhodopsin function, as expressed by a light stimulated release of calcium ion and the kinetics of the metarhodopsin I to metarhodopsin II transition. By this approach, the dependence of the transduction process on membrane microenvironment and the role of the disc membrane in this process can be elucidated.